The present invention relates to microlenses, and more particularly to liquid microlenses.
Most tunable microlenses are either gradient index (GRIN) lenses with the refraction index controlled electrostatically or flexible polymeric lenses with the shape controlled mechanically. Both technologies have inherent limitations that impose severe restrictions on the performance of these existing tunable microlenses.
Tunable gradient index lenses have inherent limitations associated with the relatively small electro-optic coefficients found in the majority of electro-optic materials. This results in a small optical path modulation and, therefore, requires thick lenses or very high voltages to be employed. In addition, many electro-optic materials show strong birefringence that causes polarization dependence of the microlens properties.
Mechanically adjustable flexible lenses typically have a substantially wider range of tunability than the gradient index lenses. However, they require external actuation devices, such as micropumps, to operate. Microintegration of such devices involves substantial problems, especially severe in the case where a two-dimensional array of tunable microlenses is required.
Attempts have also been made to use other technologies to produce tunable microlenses, such as liquid microlenses controlled through self assembled monolayers (SAMs). Some of these attempts are described in U.S. Pat. No. 6,014,259 to Wohlstadter, issued Jan. 11, 2000, the entirety of which is hereby incorporated by reference herein. Microlenses utilizing self assembled monolayers, however, also suffer from several problems, including severe limitations on material selection and strong hysteresis leading to the failure of the microlens to return to an original shape after a tuning voltage is disconnected. Additionally, none of the above-described microlenses allow for both lens position adjustment and focal length tuning.
A tunable liquid microlens includes an insulating layer, a droplet of a transparent conducting liquid disposed on a first surface of the insulating layer and a plurality of electrodes insulated from the droplet by the insulating layer. The plurality of electrodes are disposed such that they may be selectively biased to create a respective voltage potential between the droplet and each of the plurality of electrodes, whereby a contact angle between the droplet and the first surface is variable and the droplet may be repositioned along the first surface. Note that by transparent it is meant transparent at the light frequency of interest, which may or may not be visible.
The tunable liquid microlens allows for both lens position adjustment and focal length tuning. In addition, the tunable liquid microlens provides greater freedom in material selection.